Fantech FG4 Hum

[dougstove]

Hi;
I built a simple Y-configuration air duct system to take cold air from the floor of 2 downstairs bedrooms, and carry it to my main stove room, half a floor higher.
It is working well, just as planned. Thanks for earlier advice on the topic.
But:
I installed a centrifugal, external rotor, Fantech FG4 in line fan to move the air.
At full speed it works well, and the fan itself is very quiet.
But when I connect it to a rheostat to give speed control, I get a pronounced electrical hum (not the fan itself, it is the power supply unit mounted on the side).

Is there anyway around this? Is there a better option to lower the speed?

When I mounted the fan (on a joist in the basement) I put a layer of inner tube between the bracket the joist as a sound damper. But I did not do anything to sound-isolate the fan from the duct work.
But most of the noise seems to be coming through the open air in any case.

Some of my family are not bothered, but the hum keeps me from sleeping.
cheers from a breezy New Brunswick.

 

[fossil]

Well, there are speed controls and then there are speed controls. I'm not an electrician, but my immediate thought is that your control isn't compatible with your fan motor. You might contact Fantech and ask them just what sort of control you should be using for that unit. Rick

ETA: I have a somewhat similar system installed, using a Fantech fan (not the same one you've got), and a wall-mounted speed control which was provided by the heating contractor that supplied & installed the fan & ducting. Works like a charm. Air flow noise (depending on fan speed), yes, but no electrical humming.

 

[daryl]

Speed controls have a small adjustment screw on them that well take the hum out most of the time.

 

[Hogwildz]

I have 2 FG6 inlines. I have set up to circulate air in the addition I am working on.
Be careful what speed controller you use, they are not meant to be used with the solid state ones I believe. I May be wrong. Read the literature that came with it, they explain it better.
Mine also hums when the power is turned down.
Fossil, would sure like any info you have on the controller your using?

 

[realstihl]

Most induction fractional hp motors will hum when using a speed controller. What will help is to not mount the motor solid to house framing. Isolate it using rubber grommets or springs. It will really help with the noise.

 

[dougstove]

Thanks. The FG4 is nominally rated for a solid state controller, but there are some mentions of hum in some FanTech tech notes.
The controller I have (CanArm) looks superficially almost identical to the ones Fantech sells for the fan, but I might try one of theirs, just in case.
The only adjustment screw I have on the CanArm controller is (I think) a setting for the minimum speed.

 

[dougstove]

Update:
Thanks for the kind advice.
I found a 'Lutron FSQ-2FH-WH' 3 speed rotary dial fan speed controller at Home Depot.
I hooked it up, and, no hum.
Reading the instructions, it seems to indicate that the 'Lutron F2-5F' might be even better, but it is only 2 speeds.
So - I do not understand the electronics, but it works.

I did mess around with the adjustment screw on my previous CanArm variable speed controller, but I could not get a combination where there was no hum and appropriate fan speed.

 

[LLigetfa]

So long as the 3 speeds are what you need, I'd say case closed. The variable speed controller I have came with the blower and it hums. I mounted the blower down in the crawlspace and isolated it with anti-vibration mount and rag coupler. I essentially only use three positions on it so a 3 speed controller would probably suit me fine. I should try the Lutron to see if I can quiet mine some.

I suggest you always start the fan on the highest speed and turn it down to the desired speed afterward.

 

[LLigetfa]

It took a while to arrive but I finally got my Lutron FSQ-2FH installed today. Bad news for me, I'm afraid. It is not compatible with my blower. Of the three speeds, it works only on High.

My original KBMS-13BV speed control made by KB Electronics produces a lot of hum at all speeds but at lower speeds the hum is worse.

 

[begreen]

Usually these controllers chop the AC waveform to control the voltage to the motor. Works for shaded pole, but not cap start or synchronous motors.

 

[dougstove]

Sorry to hear it did not work. With my previous Cantech variable speed controller, the fan hum was worst at low speed as well; a full speed there was little hum.
For my Fantech fan, the Lutron solved the problem.

 

[LLigetfa]

Well, I put back the KB and put the Lutron on my ceiling fan instead so it's not a total waste of money and effort. None the less, it is disappointing.